Dr Jonathan Flowerdew

Jonathan is a research scientist focusing on the interaction between ensembles and data assimilation for convective-scale weather forecasts.

Areas of expertise:

Generation of initial perturbations for ensemble forecasting

Ensemble data assimilation

Ensemble verification

Ensemble calibration and combination

Current activities

Recent increases in computing power have made it possible to run local weather forecasts with horizontal grid spacings of one or two kilometres. This allows the explicit simulation of convection, improving predictions of severe weather such as heavy rainfall. However, forecasts at these scales can be very uncertain, and ensembles are needed to predict the range of outcomes which might occur in any given situation. The quality of such forecasts also depends on assimilating information from high-density observations such as radar. This requires knowledge of the flow-dependent convective-scale structure of the uncertainty in the previous forecast.

Jonathan's research focuses on the interaction between ensembles and data assimilation at the convective scale. The Met Office ensemble system, MOGREPS, has recently been extended with a 2.2km ensemble to sample convective-scale forecast uncertainty over the UK. On the one hand, this predicts flow-dependent covariances which could improve convective-scale data assimilation. On the other hand, data assimilation methodologies such as 4D-Ensemble-Var might provide better initial perturbations for MOGREPS-UK, improving the quality of both the ensemble forecast and the covariances it provides to data assimilation.

Jonathan's previous work at the Met Office covers several areas of ensemble forecasting. He developed an ensemble forecasting system for coastal storm surges, which has been extended to provide forecasts up to seven days ahead. He worked on the initial condition perturbations for the MOGREPS global ensemble, in particular the system which matches the ensemble spread to recently-measured forecast error. This in turn required constructing accurate estimates of the error variance of ATOVS brightness temperature observations, with requirements that differ from standard data assimilation. As part of the
THORPEX and
GEOWOW collaborations, he developed a scheme for calibrating the statistical reliability of ensemble forecasts whilst preserving their spatial structure, and evaluated the benefit of combining 15-day ensemble forecasts from different operational centres.

Career background

Jonathan joined the Met Office in 2006, after completing a DPhil at the
University of Oxford on the use of nudging and feature tracking techniques to evaluate climate model cloud. Prior to that, he spent two years working on graphics, audio and system device driver software for digital TV. Jonathan studied physics as an undergraduate, again at the University of Oxford.